This invention relates to a tentering machine for a cloth web, comprising a driven feed roller for the cloth web disposed above the needle chains, and members for spreading the edges of the cloth web, and two driven needling rollers for applying the edges of the cloth web to the needle chains, together with a device for sensing the edge of the web.
In previously known tentering machines the cloth web feed roller is spaced in front of the needling position (needling rollers) in the entry area of the machine so that what are known as unrolling fingers may for instance be disposed between said roller and the needling rollers, for spreading the web edges, together with a device for scanning the edges of the cloth web. In such cases the feed roller is generally in a plane above that wherein the web is conveyed by the needle chains. A web to be needled thus easily runs with a downward inclination from the feed roller to the needling position; the web edges can be spread out by the spreading members, and the edge-sensing device can be used to set the two lateral needle chains (with their rails) to the present width of the incoming cloth web. Parallel with the width adjustment of the needle chains there is at the same time an adjustment of the needling roller disposed above each needle chain.
It has now been found that after leaving the feed roller a cloth web to be needled hangs arcuately across its width, and the spreading elements engaging the web edges do not affect this condition. Under these conditions, it is customary to arrange the chain rails diverging, and the spreading rollers are also strongly diverging and distort the web. With broad and heavy webs of cloth this arcuate hanging may have an effect such that the web under its own weight will slip out of the spreading members (e.g. unrolling fingers) and possibly out of the needling rollers. Nor can any support for the web in its central area, ignoring the constructional expense involved, do much to change this tendency.
When with these known constructions the control according to the width of the incoming cloth web is effected by the sensing device (at the edges of the web), because of the arcuate handing of the web firstly there can be no adaptation to the exact width, and secondly the web edges will run extremely unevenly and hence make sensing of such edges extremely difficult. This has the consequence that the gap adjustment for the two needle chains and hence of the two needling rollers is affected in a very unfavorable manner, with the chain guiding elements travelling much closer together than is necessary. Since the sensing device for the edges of the cloth web usually lies between the spreading members and the needling rollers, the web must also usually cover a considerable distance before it can be needled, so that the spreadout edges of the web can at least partly roll up again, and also in particular diverging of the chain rails makes a large difference between the width at the sensing position and at the needling position, making the needling imprecise.